The present invention relates to an inertial stabilizing system for a platform which is supported on a carrier moved dynamically in a high-frequency and low-frequency manner, having a base which is arranged between the carrier and the platform and which is mounted on the carrier by way of a damping device in a high-frequency vibration-insulated manner, on which base the platform is arranged by at least one control circuit in an adjustably movable manner, which control circuit comprises an inertial sensor which senses the actual movements of the platform, a controller which forms an adjusting signal from the control deviation depending on the actual-desired position difference of the platform, and an adjusting device which is controlled by the adjusting signal and acts between the base and the platform.
Inertially controlled stabilizing systems, as used, for example, for sighting or imaging equipment on board a helicopter or another moving carrier structure, for the purpose of the azimuth stabilization, usually comprise a coupling network which consists of several control loops and by means of which a relatively slow azimuth drive for the rough (or coarse) adjustment of the sighting device is caused to follow a position-controlled fine drive for the platform to be stabilized, for example, a low-inertia deflecting mirror arranged in the line of sight. Stabilizing systems of this type, as known from German Patent Documents DE 31 00 951 A1, DE-OS 20 33 871, European Patent Document EP 0 256 592 A2 or European Patent Document EP 0 068 932, when the control quality is sufficient, require a very high control bandwidth and high control expenditures in order to control the low-frequency as well as high-frequency interference movements of the carrying structure. In the case of a helicopter these include the relatively slow flight path changes as well as the higher-frequency vibrations which result from the rotation of the rotor. In this case, the high-frequency and the low-frequency motion components of an inertia platform can be sensed separately from one another by acceleration sensors, see, for example, German Patent Document DE 34 33 189 A1.
In contrast, in the case of known stabilizing systems of the 0 initially mentioned type, for reasons of a constructional simplification of the control network, damping elements with a relatively soft damping characteristic are arranged between the carrying structure and the base of the stabilizing system. These damping elements absorb the higher-frequency motion components of the carrying structure so that only the low-frequency interference movements must still be controlled by the control loops and the pertaining actuating drives acting between the base and the platform. The difficulty that exists in the case of such damped systems is that the dampers have a low frequency selectivity and the reaction forces which result from the control movements of the actuating drives and react on the dampers induce an additional damper deformation and, as a result, an undesired control deviation. This undesired control deviation distorts the controller output so that positioning errors, post-vibrating of the platform in the case of a step function, and phase shifts occur in the control behavior which may drive the system into the resonance frequency. Although this effect may be attenuated by a reduction of the control amplification, this takes place at the expense of a sufficiently high control speed and thus of the control quality.
It is an object of the invention to provide an inertial stabilizing system of the initially mentioned type in such a manner that the damper-induced control errors are reduced in a constructionally simple manner and the control quality and the control speed are increased considerably.
This and other objects are achieved by the present invention which provides an inertial stabilizing system for a platform which is supported on a carrier moved dynamically in a high-frequency and low-frequency manner, comprising a base between the carrier and the platform, a damping device which connects the base to the carrier in a high-frequency vibration-insulated manner, and at least one control circuit, coupled to the platform. The platform is arranged on the base in an adjustably movable manner in response to the control circuit. The control circuit includes an inertial sensor which senses the actual movements of the platform, a controller which forms an adjusting signal from a control deviation dependent on a difference between an actual position and a desired position of the platform, and an adjusting device which is controlled by the adjusting signal and acts between the base and the platform, a further sensor which senses low-frequency motion components of the damping device between the carrier and the base and generates a corresponding output signal, and a control circuit element which is connected behind the further sensor and, for the formation of the control deviation, reduces the difference between the actual position and the desired position according to the output signal of the further sensor.
According to the invention, for reducing the damper-induced control error, it is not the control amplification and thus the control speed in general that is reduced, whereby the system would operate more sluggishly even in the case of smaller control deviations. Rather, the control gradient of the control network is modified as a function of the frequency and the amplitude of the sensed damper movements in such a manner that only when the limit frequency of the stabilizing system is exceeded, an intervention takes place into the control action according to the damper deformations generated by the control operation itself, whereas the high-frequency damper movements caused on the carrier side are without any influence on the control operation so that the control amplification is fully maintained up to an upper limit specified by the damper function. As a result, the interference effects which are caused by the system and by the low frequency selectivity of the dampers are reduced in a very simple and effective manner and a high control accuracy and control speed are ensured.
In an advantageous further development of the invention, the damper movements are scanned in a non-contact manner with a view to a low-wear construction of the sensor. In certain embodiments which have a simplified construction, the sensor comprises motion meter means sensing the damper movements and a low-pass filter which is connected behind it and which electronically filters out the higher-frequency motion components of the damping device.
In certain embodiments, a multi-axis stabilization is provided which has several sensors which sense the low-frequency motion components of the damping device in each case in different stabilization axes.
In certain embodiments, a network is used for azimuth stabilization which includes several control circuits which are coupled with one another and which has a coarse drive which follows a position-controlled fine drive, and only a single common sensor which senses the low-frequency motion components of the damping device with respect to the azimuth axis is assigned to all of the azimuth control circuits.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.